1. Field of the Invention
This invention relates to novel polyindanebisphenols which are useful in the preparation of thermosetting polymers and thermoplastics. The polyindanebisphenols (“PIBP”) are prepared under acidic conditions from p-2-isopropenylphenol (“IPP”) and 1,3-, 1,4-, or 1,2-diisopropenylbenzene (“DIPB”) in quantitative yield. Molecular weight is controlled by the ratio of p-2-isopropenylphenol to diisopropenylbenzene. When copolymerized with other commercial resins such as cresol novolac epoxies, PIBP based polymers are characterized by high glass transition temperature (“Tg”), low dielectric constant, low moisture absorption, low coefficient of expansion, low cost, and can be processed on equipment typically used for the production of epoxy based laminates.
2. Description of the Prior Art
Phenolic-based polymer resins such as cresol-novolacs are commonly used in the production of thermosetting polymers for electronics (printed wiring boards, encapsulents, molding compounds, electrical insulation), reinforced plastics, including fiber reinforced plastics (“FRP”), aerospace, coatings (industrial, can), and adhesives. Previously available polymers based, e.g., on cresol novolac epoxies, suffer from a number of drawbacks. These include: (1) 1-2% moisture absorption; (2) low Tg; (3) undesirably high dielectric constant and (4) brittleness.
The importance of these properties can be appreciated by considering, for example, that for polymers, as the temperature of the polymer increases, one or more temperature points are passed at which there is a modulus loss due to a glass transition. Each such temperature point is thus described as a glass transition point or Tg. Therefore, a high Tg is a desirable feature permitting a printed wiring board or similar such construct to operate at higher temperatures, e.g., in an environment that includes active electrical and/or electronic components, while maintaining its structural integrity.
These problems can be overcome by using a phenolic based resin which has inherently low moisture absorption, high Tg, and low dielectric constant. Polyindanebisphenol (“PIBP”) is particularly well suited to overcome these drawbacks because of the inherent stiffness of the indane polymer backbone and the hydrophobic nature of the polymer. However, due to the limitations of the previously available synthetic schemes, which resulted in prohibitive costs, PIBPs have not gained ready commercial acceptance for such purposes.
The synthetic chemistry of the polyindanes can be best appreciated by first considering the synthesis of a “polyindanebisphenol” having a single repeat unit. For example, 1,1,3-trimethyl-3-(p-hydroxyphenyl)-5-indanol (“TMHPI”), as shown below: is well known and has been utilized to prepare numerous thermosetting and thermoplastic polymers (U.S. Pat. Nos. 4,175,175, 5,145,926 and 4,988,785; Wilson, J. C., 1975 Journal of Polymer Science, Polymer Chemistry Edition, vol. 13, 749; Y. Imai and S. Tassavori, 1984, J. Polym. Sci., Polym. Chem. Ed., 22, 1319. However, none of these have attained a commercial status.
TMHPI is prepared from the precursor IPP, which is obtained first by cracking bisphenol A, having the following formula: 
The cracking of bisphenol A is optionally conducted under acidic or basic conditions (e.g., in the presence of NaOH at 220° C.), yielding IPP, plus phenol; having the following formulas. 
The fact that the cracking process yields a mixture containing phenol, as a contaminant, has heretofore been considered a serious shortcoming of this process. IPP is not only heat sensitive, but it will readily polymerize under cationic, anionic, and free radical conditions. Consequently, while it has heretofore been taught that isolation of phenol from IPP is required to produce TMHPI, the isolation of IPP from phenol is in fact difficult to achieve in sufficient yield. After isolation of IPP, dimerization can then be conducted under acid conditions at mild temperatures to produce TMHPI. Thus, there is a longstanding need in the art for a method of avoiding the isolation of IPP from phenol in the preparation of indanes that are derived from IPP.
In addition, polymers based on TMHPI do not provide significant improvements to the parameters of moisture absorption, Tg, dielectric constant and brittleness. For example, when comparing similar polymers based on Bisphenol A or TMHPI, there is only a modest increase (10-30° C.) in glass transition temperature or Tg. For example, when TMHPI was polymerized with an equimolar amount of 4,4′-dichlorodiphenylsulfone to yield a polyethersulfone, a Tg of 215° C. was reported, which is only 30° C. higher than the commercial polyethersulfone-based on Bisphenol A (Tg=185° C.). In another example, of TMHPI shortcomings, when TMHPI is polymerized with the diglycidyl ether of tetrabromobisphenol A, a composition used for the preparation of flame retardant printed wiring board laminates, a glass transition of only 142° C. was obtained (U.S. Pat. No. 4,672,102). For this reason, polymers based on the TMHPI-type of indane structure have not achieved commercial success. Attempts to overcome these shortcomings have also led to investigation of polyindane compounds. The preparation of polyindane from the various DIPB compounds has been known since the late 1950's (Y. V. Mitin, N. A. Glukhov, Dokl., 1957, akad. Nauk, SSSR 115, 97; H. Brunner, A. L. Pallwel, D. J. Walbridge, 1958, J. Polym. Sci. 28, 629).
One class of polyindanes are the “unfunctionalized” polyindanes, i.e., polyindanes lacking additional functional moieties capable of crosslinking or curing in the presence of other potential copolymer/co-monomer resins, e.g., epoxies. Such unfunctionalized polyindanes can be prepared from a number of precursors, under cationic conditions, using either Lewis or Bronsted acids (O. Nuyken, G. Maier, D. Yang, M. Leitner, 1992, Makromol. Chem., Macromol. Symp. 60, 57-63; 0. Nuyken, M. B. Leitner, and G. Maier, 1992, Makromol. Chem. 193,487-500; F. Gruber, O. Nuyken, 1989, Makromol. Chem. 190, 1771-1790; F. Gruber, O. Nuyken, 1989, Makromol. Chem. 190, 1755-1770 and O. Nuyken, M. B. Leitner, G., Maier, 1991, Makromol. Chem. 192,3071). Thus, any functionality which can be conveniently converted to the isopropenyl functionality is a suitable precursor to an unfunctionalized polyindane. For example, either of the following structures can be chemically converted into unfunctionalized polyindane: wherein X1 and X2 can be the same or different and can independently be any of Cl, OH, OCH3 and/or OCOCH3. Formula A is 1,4 diisopropenylbenzene and Formula B can be, e.g., ,′-dihydroxy-1,4, diisopropylbenzene, 1,4-bis(2-chloroisopropylbenzene), 1,4-bis(2-methoxy isopropylbenzene and 1,4-bis(2-acetoisopropyl benzene). The resulting polyindane has the formula: wherein “n” is an integer representing the number of repeats of the bracketed moiety or unit. However, this class of polyindane compounds has also, heretofore, failed to provide any practical and economical solutions for any of the above-mentioned problems in the art. Nevertheless, the compounds of Formulas A and B are readily employed as precursers to the compounds of the present invention, as described hereinbelow.
In particular, unfunctionalized polyindanes are claimed to have a Tg range from 220-320° C. and a decomposition temperature of 450° C. In fact, the art has described a broad range of molecular weights and glass transition temperatures, which attest to the difficulty in preparing pure polyindanes without some level of undesirable unsaturation. However, no commercial products have resulted from these efforts, due to the many shortcomings of this class of compounds. For example, the heretofor reported process is known to provide only low molecular weight polyindanes of this class, i.e., molecular weights of substantially less than 5,000 Dalton (see, e.g., O. Nuyken, et al., 1992, Makromol. Chem. 193, 487-500). Despite the suggestion that higher molecular weights might be obtained (e.g., Fritz et al., 1972, J. Polymer Science Part A-1, 10:2635-2378; D'Onofrio, 1964, J. of Applied Polymer Science 8:521-526; and Brunner et al., U.K. Patent No. 864,275, the previously provided polyindane polymers have been described as brittle, confirming undesirable mechanical properties.
In addition, these unfunctionalized polyindanes have other major drawbacks specifically related to printed wiring board applications. For instance, these compounds have no gel point, cannot be cured and do not crosslink. Thus, they exhibit unacceptably high coefficients of linear expansion and, without a curing step, cannot be used in traditional processes to produce laminate compositions. Further, polymers prepared from unfunctionalized polyindanes melt and flow at the temperatures used for soldering. In yet a further disadvantage, unfunctionalized polyindanes cannot be reacted chemically with other resins used to produce printed wiring boards.
“Functionalized” polyindanes were also tried in an attempt to produce less brittle polyindanes suited for the preparation of thermoplastics and thermosets. These were prepared by controlling the molecular weight and introducing functionality into the polymer, e.g., by introducing various substituent moieties to prepare polyindane derivatives. This strategy has been employed for the preparation of telechelics having terminal R groups, where R was CH3, NO2, NH2, CO2H, NCO, and COCl (O. Nuyken, D. Yang, F. Gruber, G. Maier, 1991, Makromol. Chem. 192:1969.
However, the available synthetic routes to obtain useful functionalized polyindanes have remained too expensive for commercial purposes. Thus, only the methyl terminated polyindanes have been directly prepared using a cationic chain growth process involving diisopropenylbenzene and 1-isopropenyl4-methylbenzene (Nuyken et al., 1992, Makromol. Chem., Macromol. Symp. 60, 57-63, Id.). Further chemical modification was necessary to obtain other functionalized polyindanes.
Thus, there remains a strong need in the art for polyindane compounds having all of the above-described desirable properties, e.g., reduced levels of moisture absorption; increased thermal stability; reduced dielectric constant and decreased brittleness, for this class of compounds, while being simple and economical to manufacture. In particular, there remains a need for functionalized polyindanes having all of the desirable properties of this class of compounds, and having a molecular weight of less than 2,000 which are not brittle and which can be reacted with other material, e.g., monomer compounds, for the preparation of thermosets and/or thermoplastics.